This invention-relates to a switchable liquid-filled vibration isolating mount used to support in a vibration isolating or damping manner a vibrator, such as a power unit and the like of an automobile.
A liquid-filled vibration isolating mount has heretofore been used as a mount for supporting a vibrator, such as an automobile engine so that vibration is not transmitted to a car body.
As a kind of such mount, it has been proposed a switchable liquid-filled vibration isolating mount in which their vibration isolating or damping characteristics are switched from one to another, in accordance with each of two kinds of vibrations in different frequency ranges including shaking vibration and idling vibration (for example, JP-A-1996-270718, JP-A-1998-238586 and JP-A-1998-184777 (Japanese Patent Laid-Open or Unexamined Publication Nos. 270718/1996, 238586/1998 and 184777/1998)).
For example, JP-A-1996-270718, discloses a mount shown in FIG. 5 herein which has the following construction.
This vibration isolating mounts includes a first rigid fixture 101; a second rigid fixture 102 having a bottomed barrel shape, a bottom wall of which is spaced apart from the first fixture 101 at a predetermined distance away in the axial direction; a vibration isolating base body 103 interposed between and joining together the first and second fixtures 101, 102, and formed of an elastic material such as rubber; a partitioner 104 and first and second diaphragms 105, 106 disposed in series in the axial direction between the vibration isolating base body 103 and second fixture 102; a main liquid chamber 107 formed between the vibration isolating base body 103 and partitioner 104; a sub-liquid chamber 108 formed between the partitioner 104 and first diaphragm 105; an outer orifice 113, and an inner orifice 114 positioned diametrically on the inner side of the outer orifice 113 both of which orifices are provided on the partitioner 104 and communicate the main and sub-liquid chambers 107, 108 with each other, which outer orifice 113 extends to a predetermined length in the circumferential direction of the partitioner 104, which inner orifice 114 is adapted to be opened and occluded by and with the first diaphragm 105; a biasing member 127 adapted to bias or elastically press the first diaphragm 105 against the partitioner 104 to thereby prevent a liquid from flowing between the inner orifice 114 and sub-liquid chamber 108; an equilibrium chamber 109 formed between the first and second diaphragms 105, 106; and a switching chamber 110 formed between the second diaphragm 106 and second fixture 102 and capable of receiving an atmospheric pressure and a reduced pressure introduced selectively thereinto, the introduction of a reduced pressure into the switching chamber 110 causing the first diaphragm 105 to be moved against a biasing force of the biasing member 127 and leave the partitioner 104, and the inner orifice 114 and sub-liquid chamber 108 to communicate with each other, whereby the orifices corresponding to the respective two kinds of vibrations in different frequency ranges can be selectively used.
In this known liquid-filled vibration isolating mount, not only the outer orifice 113 but also the inner orifice 114 opened and occluded by and with the first diaphragm 105 are annularly formed. Because the inner orifice 114 also has some significant length in circumferential direction, a resulted flow resistance suppresses the liquid flow therein. Consequently, because the liquid also flows in the outer orifice 113, a sufficient vibration damping effect cannot be obtained in the inner orifice 114.
In order to occlude the inner orifice 114, a central portion of the first diaphragm 105 is pressed against a lower face of the partitioner 104 by the biasing member 127. In detail, the planar central portion of the first diaphragm 105 abuts on the planar portion of the partitioner 104, which planar portion is around an opening 114a of the inner orifice 114 and which planar portion is on the side of the sub-liquid chamber 108. The inner orifice 114 is occluded only by such a plane-to-plane abutting. Therefore, when a pressure of, for example, the interior of the main liquid chamber 107 becomes suddenly high, or when a slight loosening occurs in the engaged portion due to a lateral deviation of the first diaphragm 105, there is the possibility that the inner orifice 114 is not sufficiently occluded.
The present invention has been made in view of the above-described problems. The present invention provides a switchable liquid-filled vibration isolating mount having basically the same construction as the above-described known liquid-filled vibration isolating mount which has inner and outer orifices, the inner orifice out of which is formed so that it can be opened and closed, and which is capable of selectively using the orifices corresponding to two kinds of vibrations in different frequency ranges, such as shaking vibration and idling vibration, the apparatus according to the invention being formed so that it can solve the aforementioned problems and retain stable characteristics thereof by improving the modes of the two orifices on the partitioner and the shape of the inner orifice-occluding first diaphragm.
The present invention is directed to a switchable liquid-filled vibration isolating mount including, just as the above-described liquid-sealed vibration isolating mount, a first fixture; a second bottomed cylindrical fixture; a vibration isolating base body joining these fixtures together; a partitioner and first and second diaphragms disposed in series between the second fixture and vibration isolating base body; main and sub-liquid chambers separated from each other by the partitioner; outer and inner orifices provided in the partitioner and communicating the two chambers with each other; a biasing member for pressing the first diaphragm against the partitioner; an equilibrium chamber formed between the first and second diaphragms; and a switching chamber formed between the second diaphragm and second fixture; the partitioner between the main and sub-liquid chambers having an opening as the inner orifice extending therethrough in the axial direction; the first diaphragm being provided with a valve body having a projection coaxial with and adapted to be fitted in the opening as the inner orifice; the switching chamber being formed so that either a reduced pressure or an atmospheric pressure is introduced thereinto to cause the valve body to be vertically moved and thereby enable the opening to be occluded or opened.
When the valve body moves away from the partitioner to cause the opening to be opened, the inner orifice is put in an operating state, so that a vibration damping operation in a frequency range set with respect to the inner orifice is carried out effectively with a liquid flow in the outer orifice suppressed.
Meanwhile, because the projection of the valve body is inserted in the opening, the occurrence of loosening of the occlusion due to a lateral deviation of the first diaphragm is prevented, so that the first diaphragm can tightly abuts at all times on the partitioner without being laterally displaced with respect to the latter. Accordingly, a sufficient occluded condition can be secured, whereby stable characteristics of the apparatus can be maintained for a long period.
The circumferentially extending outer orifice may extends along a circular, elliptic or polygonal shape, or some other complete annular shape; or a shape of a part of any of these shapes.
In this vibration isolating mount, the outer orifice may be formed as a shaking vibration damping member, and the inner orifice as an idling vibration damping member.
A flow passage of the outer orifice is formed to a length larger than that of a flow passage of the inner orifice, and/or a cross-sectional area in the axial direction of the vibration isolating mount of the former flow passage can be set smaller. Since the outer orifice is thus formed, the outer orifice can be used more suitably for damping vibration of a smaller frequency and a larger wavelength as compared with the inner orifice.
It is preferable from the viewpoint of the manufacturing of this mount to provide the inner orifice in a central portion of the partitioner, and the valve body in a central portion of the first diaphragm correspondingly.
When the projection of the valve body in this switchable liquid-filled vibration isolating mount is provided so that at least a part of this portion is positioned in the opening of the partitioner even during the introduction of a reduced pressure into the switching chamber, there is not the possibility that the valve body completely leaves the opening. Therefore, the displacement preventing effect is reliably obtained. In addition, when a lateral deviation preventing unit is provided on an outer circumferential part of the projection of the valve body, the valve body abuts on a lower face of the partitioner without being laterally deviated, so that the abutting of the valve body occluding the inner orifice is not loosened. When this lateral deviation preventing unit is engaged with the inner orifice, the lateral deviation preventing effect is obtained more reliably.
In this switchable liquid-filled vibration isolating mount, a cap-like member joined to the second diaphragm and defining an inner boundary of the equilibrium chamber is suitably formed of a member fitted firmly in a lower portion of the valve body. Owing to such a cap-like member, the valve body is supported so as to maintain a predetermined shape thereof, and moved vertically in accordance with the switching of the introduction of a reduced pressure into the switching chamber to that of an atmospheric pressure thereinto, and vice versa, whereby the. opening and closing of the above-mentioned opening is effected reliably.
By use of a stopper member for restricting a downward movement of the valve body during the introduction of a reduced pressure into the switching chamber, a cross-sectional area of an opening formed between the second orifice and valve body is always kept constant at the time of introduction of a reduced pressure into the switching chamber. Thus, the vibration damping characteristics of the mount is kept stable.